Plants poisonous to Horses

Horses are highly sensitive to certain plants, and some that may seem harmless to humans or other animals can be deadly to them.

Here’s a comprehensive list of known poisonous plants in the UK that can affect horses. I’ve categorized them for clarity:

1. Trees and Shrubs

Yew (Taxus baccata)

All parts, especially leaves

Sudden death from cardiac failure; very toxic

Rhododendron / Azalea

Leaves and flowers

Colic, vomiting, diarrhea, cardiac issues

Oleander (Nerium oleander)

All parts

Heart arrhythmia, colic, death

Laburnum

Seeds, pods, leaves

Vomiting, diarrhea, weakness, collapse

Horse Chestnut (Aesculus hippocastanum)

Seeds (conkers), leaves

Weakness, colic, ataxia

Cherry (wild Prunus spp.)

Leaves, especially wilted

Cyanide poisoning, sudden death

Elderberry (Sambucus nigra)

Leaves, stems, unripe berries

Vomiting, diarrhea, respiratory distress

Privet (Ligustrum spp.)

Leaves, berries

Gastrointestinal upset, weakness

2. Garden and Ornamental Plants

Foxglove (Digitalis purpurea)

Leaves, flowers

Heart problems, weakness, death

Buttercup (Ranunculus spp.)

Fresh plant

Mouth irritation, colic (less toxic when dried)

Daffodil (Narcissus spp.)

Bulbs

Colic, vomiting, cardiac issues

Lily-of-the-valley (Convallaria majalis)

All parts

Heart arrhythmias, weakness

Hemlock (Conium maculatum)

All parts

Neurological signs, respiratory failure, death

Deadly Nightshade / Belladonna (Atropa belladonna)

Leaves, berries

Dilated pupils, colic, nervous system issues

Ragwort (Senecio jacobaea)

Leaves, flowers

Liver failure (chronic), colic, photosensitization

Bracken (Pteridium aquilinum)

Shoots, fronds

Thiamine deficiency, neurological disease (long-term ingestion)

Autumn Crocus (Colchicum autumnale)

Bulbs, flowers

Severe gastrointestinal upset, kidney and liver damage, death

3. Pasture / Field Plants

Hemlock Water Dropwort (Oenanthe crocata)

All parts

Sudden death, colic, tremors

Buttercups (Ranunculus spp.)

Fresh leaves

Mouth irritation, drooling, colic

Bracken

New shoots

Chronic poisoning: nervous disorders

Foxglove seedlings in pasture

All parts

Heart failure, weakness

Wild Cherry / Prunus

Wilted leaves in pasture

Cyanide poisoning

4. Plants Common in Fields

Hemlock (Conium maculatum)

All parts

Neurological signs, respiratory failure

Ragwort

Leaves & flowers

Chronic liver failure, jaundice

Hellebore

All parts

Vomiting, diarrhea, heart irregularities

Bracken (Pteridium)

Fronds, rhizomes

Neurological, liver damage

⚠ Key Points for Horse Owners

Many plants become less toxic when dried, but some (like ragwort) remain toxic in hay.

Even small amounts can be dangerous, especially for sensitive horses.

Regular pasture management is essential: remove poisonous plants, especially ragwort, yew, hemlock, and bracken.

Symptoms of poisoning: colic, depression, weakness, staggering, drooling, laboured breathing, sudden death.

Immediate veterinary attention is crucial if ingestion is suspected.

Here’s a list of plants that can be found in Cornwall (and broadly in the UK) that are poisonous to horses — important to check for if you keep horses or grazing animals in the region. (Note: while not every UK plant grows everywhere in Cornwall, these are the ones horse owners commonly worry about on Cornish pastures, hedgerows and adjoining land.)

🌱 Key Poisonous Plants to Watch for in Cornwall

1. Ragwort (Senecio jacobaea)

One of the most common poisonous weeds in UK pasture, including Cornwall.

All parts are toxic and especially dangerous when dried (e.g., in hay). Eating even small amounts over time can cause severe liver damage.

Although horses usually avoid it fresh due to its bitter taste, wilted or hay‑mixed ragwort is much more palatable.

2. Yew (Taxus baccata)

Frequently found in hedgerows and gardens that border pastures.

Extremely toxic: all parts — leaves, seeds, berries and clippings — contain toxins that can cause heart failure and sudden death, even in small amounts.

3. Sycamore (Acer pseudoplatanus)

Common tree in many Cornish fields and edges.

Its seeds (samaras) and possibly leaves contain a toxin (hypoglycin A) linked to atypical myopathy, a serious and potentially fatal muscle disease in horses.

4. Oak (Quercus spp.) and Acorns

Acorns and young leaves contain tannins that can cause colic, liver damage and kidney problems if eaten in large amounts. Horses often like acorns, making this a notable autumn risk in Cornwall.

5. Hemlock (e.g., Water Dropwort / Cowbane)

Found in damp ground, river margins, and occasionally low‑lying pasture land in Cornwall.

All parts are highly toxic to horses (and other animals); ingestion can lead to muscle paralysis, respiratory failure or death.

6. Privet (Ligustrum spp.)

Common ornamental hedge plant that can appear near grazing fields.

Leaves and berries can cause gastrointestinal and nervous system problems, including colic, weakness or worse if eaten.

7. Rhododendron / Laurel

Often found in garden edges and hedgerows close to pasture.

Very toxic even in relatively small amounts; can affect the digestive and respiratory systems, and cause serious illness or death.

8. Bracken Fern (Pteridium aquilinum)

May occur on rough pasture, moorland edges and scrubland in Cornwall.

Contains toxins that can lead to thiamine deficiency and neurological signs if ingested regularly over time.

⚠️ Less Common but Toxic If Present

(May occur in some Cornish fields or nearby gardens)

Ragwort is specifically highlighted by Cornwall Council as an injurious weed that landowners should control on grazing land used for horses.

Many of these toxins remain poisonous even when dried or cut, so check hay and forage carefully.

Regular pasture management — removing poisonous plants before flowering and seed set — is key to reducing risk.

Summary of Poisonous Plants and effects

Ragwort

• Liver damage

Yew

• Heart failure

Sycamore

• Atypical myopathy

Oak/acorns

• Colic, kidney/liver problems

Hemlock

• Nervous/respiratory failure

Privet

• GI & nervous effects

Rhododendron/Laurel

• GI/respiratory problems

Bracken

• Neurological deficiency

What To Do

✔ Walk your fields regularly, especially edges and fence lines.

✔ Remove or fence off toxic plants before horses have access.

✔ Check hay and forage for ragwort and other weeds.

✔ Contact your vet immediately if you suspect ingestion.

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